NASA's Earth Observation System Data Information System

by Kevin Schaefer

Over the years, NASA has collected a great deal of Earth science data from
dozens of orbiting satellites. With time, these data collections have
scattered among many archives that vary significantly in sophistication and
access. NASA risked losing valuable, irreplaceable data as people retired,
storage media decayed, formats changed and collections dispersed. Scientists
began to spend more time searching for data than performing research.

Today, NASA's Office of Mission to Planet Earth, which leads the agency's
Earth science research, continues to collect data. This office operates 11
active satellites and instruments, which together produce 450 gigabytes (Gb) of
data each day. Landsat alone, one of NASA's most popular sources of remote
sensing data, produces 200 Gb of raw data per day. In 1997, NASA will launch
the first of many Earth Observation Systems (EOS) satellites and instruments
that will double the daily production of raw data. EOS will produce 15 years
of global, comprehensive environmental remote sensing data.

To handle the size and variety of data now available and to promote
cross-discipline research, NASA created EOSDIS, which drastically reduces the
time spent searching for relevant data, allowing scientists to focus their
research efforts on changes in the Earth's environment. EOSDIS allows
scientists to search many data centers and disciplines quickly and easily,
quickening the pace of research. The faster the research, the more quickly
scientists can identify causes of detrimental environmental effects, opening
the way for policy- and lawmakers to act at international, national and local
levels.

The well-known hole in the ozone layer above the Antarctic illustrates the
process from research to policy to law. Researchers first discovered the ozone
hole when lofting a weather balloon from an Antarctic research station. But
NASA's NIMBUS 7 satellite had the necessary instruments, so why hadn't it
detected the hole? Scientists quickly discovered that the calibration
algorithm routinely dropped low ozone values as "noise." When they retrieved
12 years of original NIMBUS 7 data, scientists verified the existence of the
hole and indicated that it had grown over the last decade. Data from
additional instruments revealed that CloroFloroCarbons (CFCs), such as Freon,
destroyed the ozone layer and created the hole. Armed with this knowledge, the
United States signed several international treaties restricting the production
of CFCs. Congress passed regulations on the production, distribution and
recovery of CFCs in the United States. As a direct result, worldwide
production of CFCs has plummeted. Today, consumers cannot openly buy Freon.
Given time, the CFCs already in the atmosphere will disperse and the ozone
layer will heal itself.

Another example of the benefits of multiple-discipline Earth science
research lies in the work of the EOSDIS Pathfinder projects, which recycle old
data from past and current satellites into new products for scientific
research. One project used old Landsat data to assess deforestation in the
Amazon basin, indicating that the true rate of deforestation closely matches
that cited by the Brazilian government, thus ending a long standing,
international debate. Now that scientists have settled the extent of
deforestation, policy- and lawmakers can act to fix it.

In yet another result of the EOSDIS philosophy, ocean dynamists recently
discovered a huge, low-amplitude wave that propagates back and forth across the
Pacific Ocean. Only a few inches high, but a thousand miles long, the wave
bounces back and forth between South America and Asia. The same scientists
also found that sea level has risen slightly over the last few years, while
other researchers detected a slight decline in total ice coverage. Are these
three phenomena related? If so, why? Only collaborative research between
atmospheric physics, ocean dynamics, meteorology and climatology can answer
these questions.

The same principles apply to regional and local, as well as national and
international, policy and law. Through EOSDIS, state and local governments can
obtain accurate data and information about water tables, flood plains, ground
cover and air quality. For example, the state of Ohio has begun using NASA
remote sensing data to monitor reclamation of strip mining sites, a task for
which the state does not have enough personnel to perform on-site
inspections.

EOSDIS does a lot more than just store and distribute Earth science data.
It also provides the operational ground infrastructure for all satellites and
instruments within the Mission to Planet Earth office at NASA. It contains
Earth science data from EOS satellites, other MTPE satellites, joint programs
with international partners and other agencies, field studies and past
satellites. It receives and processes the raw data from the satellites. After
initial processing, EOSDIS delivers the data to the Distributed Active Archive
Centers (DAACs) for further processing, storage and distribution. EOSDIS also
includes mission operations and satellite control.

Distributed Active Archive Centers

The DAACs serve as the interface between EOSDIS and the user community.
Each DAAC concentrates on a specific discipline of global change and Earth
science, storing all raw satellite data received from the Data Production
Facility and processing the raw data into usable products. The products are
then distributed on a variety of media, such as magnetic tape or CD-ROM. Users
query DAAC content through the Internet, viewing low resolution, browse images
of the desired data. EOSDIS has nine DAACs:

National Snow and Ice Data Center (NSIDC), at the University of
Colorado in Boulder, specializes in the Earth's cryosphere.

Oak Ridge National Lab (ORNL), jointly funded with the Department of
Energy in Oak Ridge, Tennessee, specializes in biogeochemical dynamics.

Socioeconomic Data Archive Center (SEDAC) at the University of Michigan
in Saginaw, specializes in integrating socioeconomic and environmental data.

The Science Computing Facilities generate the software algorithms that
DAACs use to transform raw satellite data into useful products and perform
quality control on DAAC products. One or more Science Computing Facilities
support each instrument on each satellite.

EOSDIS Core System

The EOSDIS core system consists of the Science Data Processing Segment, the
Flight Operations Segment and the Communications and Systems Management
Segment.

The Science Data Processing Segment handles all data production, archive
and distribution through the Information Management Service, the Planning and
Data Processing System, and the Data Archival and Distribution Services. The
Information Management Service performs data search, access and retrieval for
the EOSDIS. The Planning and Data Processing System processes the raw data
into the standard products offered by the EOSDIS. The Data Archival and
Distribution Service permanently stores all data received or produced by
EOSDIS.

The Flight Operations Segment, consisting of the EOS Operations Center, the
Instrument Support Terminals and the Spacecraft Simulator, supports the EOS
satellites and instruments. The Operations Center commands and controls the
operation of EOS satellites. The Instrument Support Terminals consist of a few
generic workstations dedicated to the command and control of specific
instruments. Generally, each instrument will have its own Instrument Support
Terminal. The Spacecraft Simulator analyzes general satellite information
stripped off the main data stream, searching for trends and problems.

The Communications and Systems Management Segment, consisting of the
Systems Management Center and the NASA Internal Network, manages schedules and
operations among the DAACs and other elements of the EOSDIS. The Systems
Management Center manages network loading, data transfer and overall processing
to optimize EOSDIS performance. The Internal Network connects all of the
permanent archives, transferring data among all of the DAACs and Science
Computing Facilities via a dedicated fiber network utilizing the asynchronous
transfer mode. The NASA Science Internet (or Internet for short) links the
general user to the EOSDIS. The Internet also links EOSDIS to data centers
outside NASA.

The EOSDIS Data and Operations System (EDOS), consisting of the Data
Interface Facility, the Data Production Facility and the Sustaining Engineering
Facility, handles all telemetry to and from the satellite and performs the
initial data processing. The Data Interface Facility is the primary
communication and data link between the ground and the satellites. The Data
Interface Facility separates the main data stream into the scientific and
system information. The scientific information goes to the Data Production
Facility, while the system information goes to the EOS Operations Control
Center and the Spacecraft Simulator. The Data Production Facility separates
the scientific data by instruments, calibrates it and attaches any ancillary
data (orbit information, for example). All data then gets transferred to the
DAACs for permanent storage. The Sustaining Engineering Facility maintains
equipment, identifies hardware trends and plans for future upgrades.

The DAACs process the data from each instrument on each satellite into
approximately 250 products. Among the many satellite projects from which
products are developed are the Tropical Rain Measurement Mission, the Ocean
Topography Experiment and Total Ozone Mapping Spectrometer. Through EOSDIS,
data products can come from field campaigns, such as the Boreal Ecosystem
Atmosphere Study; from satellites operated by other agencies, such as NOAA's
Geostationary Orbit Environmental Satellite; and from past NASA missions and
programs. Users can locate data products by discipline, DAAC, Earth location,
instrument, satellite or time. EOSDIS allows any data format, but uses the
Hierarchical Data Format, developed by the National Center for Supercomputing
Applications, as the standard.

NASA released Version 0 of the EOSDIS to the general public in 1994.
Version 0 connects all the DAACs with some elements of the Science Data
Processing Segments, primarily the Information Management Service. Version 0
consolidates 12 distinct data systems and allows users to locate and order data
products at eight DAACs (SEDAC will come on line later this year). Through
Version 0, users can also link to NOAA's Satellite Active Archive. Version 1,
due for release in February 1996, will include all functional elements of the
EOSDIS, but not at full capacity. Version 2, due for release in November 1997,
will bring the EOSDIS up to full capacity. Minor upgrades between versions
will fix small problems, improve specific services and add new products.

Anyone can access the EOSDIS via the Internet with telenet or via modem.
One can access Version 0 from a computer that runs UNIX, X-Windows or VT100.
Users can search through the EOSDIS archives in a variety of ways: by
scientific discipline, satellite or product name. One can limit the search to
specific regions on the Earth or specific dates. To help in selection, EOSDIS
allows users to preview low-resolution browse images before ordering the data
product. Data set descriptions also help users choose applicable products. A
help desk at each DAAC takes data orders and troubleshoots problems.
Kevin Schaefer is with NASA Headquarters in Washington, DC.